Multicontrast photographic emulsions containing cyanine dyes



Aug. 2, 1960 B. H. CARROLL MULTICONTRAST PHOTOGRAPHIC EMULSIONS CONTAINING CYANINE DYES Original Filed Jan. 18, 1957 2 Sheets-Sheet 1 DENSITY l I I I i I 1 6 0 38 L O L58 z'ozba LOG EXPOSURE DENSITY I v :w a H v 0 038 L0 as 20 236 L06 EXPOSURE BurtHCarroll INVENTOR.

AT TORNEYS Aug. 2, 1960 Original Filed Jan. 18, 1957 DENSITY DENSITY aol B. H. C MULTICONTRAST PHOTOGRAPHIC EMULSIONS ARROLL 2,947,631

CONTAINING CYANINE DYES 2 Sheets-Sheet 2 I I l I l I I I I I l I I 2E0 258 L 06 EXPOSURE LOG EXPOSURE BurtIiCarroll INVENTOR. fifiuw ATTORNE'I'S United States MULTICONTRAST PHOTOGRAPHIC EMULSIONS CONTAINING CYANINE DYES Original application Jan. 18, 1957, Serial No. 634,944. Divided and this application Mar. 3, 1958, Ser. No. 718,726

8 Claims. (Cl. 96-106) This invention relates to photographic silver halide emulsions, and more particularly, to photographic materials having various degrees of contrast, depending upon the spectral distribution of the exposing source.

This application is a division of my application Serial No. 634,944, filed January 18, 1957. Photographic silver halide emulsions intended primarily for the manufacture of printing materials having various degrees of contrast under the same conditions of development have been prepared in the past by coating in layers, or mixing together, two different silver halide emulsions having different contrasts (gamma). Thus, for example, an emulsion which has high contrast and is sensitive to blue, such as a silver chloride emulsion, can be mixed with an emulsion which has low contrast and is sensitive to green, such as a spectrally sensitized silver bromide emulsion. If such a composite emulsion is exposed to light passing through a blue-green filter, the emulsion works normally and is suitable for negatives of normal gradation or contrast. If, however, it is desired to print from a negative with a wide range of densities, the light which acts upon the high-contrast emulsion is cut off by means of a filter permeable only to green, and a normal picture is obtained by means of the low-contrast emulsion. On the other hand, if it is desired to print from a negative with but little contrast, the light which acts upon the low-contrast emulsion is cut off by means of a filter permeable only to blue and a normal picture is obtained by means of the high-contrast emulsion.

One of the major problems in multicontrast materials. however, is to secure a suitable balance of sensitivities and density scales in the two emulsions so that it is possible to print a range of contrasts between the two extreme values of contrast. If the sensitivities and scales of the two components through the appropriate filters are not equal, attempts to print intermediate contrasts by a mixture of green and blue light will result in badly distorted characteristic curves and very poor tone reproduction.

The above method for making photographic prints which vary in contrast has not been found useful in the preparation of multicontrast emulsions of long scale which will reproducenegatives of great density range in the form of prints to be viewed by transmission. Furthermore, when mixtures of emulsions of different composition and development rates are used, the results are sensitive to development conditions.

One of the methods proposed for making multicontrast emulsions which are useful in the manufacture of transparencies is to add to the emulsion a material absorbing a region of the spectrum to which the emulsion is sensitive in sutficient quantity so that the contrast for that region is lowered. This insures that the scale of the emulsion for this region will be lengthened, since the con trast is lowered without any loss of maximum density. It also provides a material which in its normal contrast range can be used for printing average negatives. In the region containing the absorber, negatives of high contrast and wide density range can be used to produce normal prints. However, such materials containing a lightatent O ice absorbing dye are quite difficult to produce since nearly all of the available light-absorbing materials have an adverse effect upon the emulsion and especially on the optical or spectral sensitizing dyes customarilyemployed. The addition of the light-absorbing dye in a concentration sufiicient to lower the contrast by one-half, which is the minimum requirement for most multicontrast applications, inevitably causes a decrease in sensitivity to the region absorbed by a factor of about ten from the absorption alone. Unless the absorber is exceptionally free from desensitizing effects, there will be serious loss of sensitivity for all regions of the spectrum, and the sensitivity in the region of low contrast will be so low that it is impossible to balance sensitivities. It has also been found diflicult to select absorbing materials which act as selectively as desired. The absorption bands of many dyes are so broad that the addition of a suflicient quantity to the emulsion to lower the contrast in the green causes a serious loss of speed in the blue region because the dye also absorbs blue. Furthermore, many of the light-absorbing dyes used in photography fail to bleach or wash out completely in processing. The sensitizing dye used must give very selective absorption for the region covered by the light-absorbing dye, since a small extension of sensitivity past the region of heavy absorption will give an unsatisfactory curve shape for the characteristic curve, with a toe of the desired contrast and a high contrast shoulder. In addition, the sensitizing dye must function satisfactorily in the presence of the lightabsorbing dye.

It is, therefore, an object of my invention to provide photographic silver halide emulsions showing varying degrees of contrast, depending upon the spectral distribution of the exposing source. Another object of my invention is to provide photographic silver halide emulsions showing varying degrees of contrast which are particularly useful in the manufacture of prints which are to be viewed by transmission. Still another object is to provide a method for making such photographic silver halide emulsions. Other objects will become apparent from a consideration of the following description and examples. According to my invention, I provide photographic silver halide emulsions showing varying degrees of contrast'by incorporating therein a light-absorbingoxonol dye containing a 3-methyl-1-sulfophenyl-2-pyrazolin-5- one nucleus or a barbituric acid (but not thiobarbituric acid) nucleus, and a spectral sensitizing dye selected from the group consisting of (1) a cyanine dye containing a 5- phenylbenzothiazole nucleus, (2) a cyanine dye containing at lease one carboxyalkyl group, (3) a cyanine dye containing at least one sulfoalkyl group, (4) a merocyanine dye containing a carboxyl group, (5) a merocyanine dye containing a sulfo group, and (6) 4-[(l,3,3- trimethyl-2(3H)-indolylidene)ethylidene] 3 methyl-l- .phenyl-2-pyrazolin-5-one. While a very high proportion of sensitizing dyes fails to sensitize satisfactorily in the presence of such'oxonol dyes, the dyes enumerated above have been found to be quite satisfactory in providing multicontrast materials according to my invention. For the purposes of my invention, the above-enumerated sensitizing dyes should have their maximum absorption in the same region of the spectrum as the oxonol dyes, and the absorption maximum of the sensitizing dyes should generally lie beyond about 480500 I'll/1., i.e., beyond the blue region of the spectrum.

The spectral sensitizing dyes which have been found to be particularly useful in my invention can beillustrated by the following:

Group A.5-phenylbenzothiazole dyes:

(1) 3,3 dimethyl 5,5,9 triphenylthiacarbocyanine bromide.

(2) 3,3 -diethy1 5,5',9 triphenylthiacarbocyanine p-toluenesulfonate.

(3) 3 ethyl 3' methyl 5,5,9 triphenylthiacarbocyanine p-toluenesulfonate.

(4) 3,3,9 triethyl 5,5 diphenylthiacarbocyanine iodide.

Group B.Carboxyalkyl cyanine dyes:

(1) Anhydro 3 [3 carboxyethyl 1 ethylthia 2-cyanine hydroxide.

(2) Anhydro l carboxymethyl 3 ethylthia 2'-cyanine hydroxide.

(3) Anhydro 3,3 dicarboxymethylthiacyanine hydroxide.

(4) Anhydro 3 carboxymethyl 1' ethylthia 2-carbo cyanine hydroxide.

(5) Anhydro 3,1 di fi carboxyethylthia 2 cyanine hydroxide.

Group C.Sulfoalkyl cyanine dyes:

(1) Anhydro 5 chloro 3 ethyl 3 8 sulfoethylthiacyanine hydroxide.

(2) Anhydro 1 ethyl 3 )8 sulfoethylthia 2 cyanine hydroxide.

(3) Anhydro 3 fl carboxyethyl 5,5 dichloro 9-ethyl-3fl-s-ulfoethylthiacarbocyanine hydroxide.

(4) Anhydro 5,5 dichloro 9 methyl 3,3

di-p-sulfoethylthiacarbocyanine hydroxide.

Group D.-Carboxy-merocyanine dyes:

(1) 3 (p carboxyphenyl) 5 [(3 ethyl 2( 3H) -benzothiazolylidene) ethylidene] rhodanine.

(2) 5 (1 n butyl 4(1H) quinolylidene) 3 carboxymethylrhodanine. I

(3) 3 carboxymethyl 5 [(3 methyl 2(3H) thiazolinylidene) ethylidene] 2 thio 2,4 oxazolidinedione. v

(4) 4 [(3 ethyl 2(3H) benzothiazolylidene) isopropylidene] 3 methyl l p carboxyphenyl-Z-pyrazolin-S-one.

Group E.Sulfo-merocyanine dyes:

('1) 4 [(3 ethyl 2(3H) benzothiazolylidene) isopropylidenel 3 methyl 1 p sulfophenyl 2-pyrazolin-5-one.

(2) 5 [(3 ethyl 2(3H) benzoxazolylidene) ethylidene] -3- 8-sulfoethylrhodanine.

(3) 4 [(3 ethyl 5 phenyl 2(3H) benzoxazolylidene) ethylidene] 3 methyl 1 -p sulfophenyl-2-pyrazolin-5-one.

(4) 5 [(3 methyl 2(3H) thiazolinylidene) isopropylidene] -3 3-sulfoethylrhodanine.

The light-absorbing oxonol dyes which have been found to be useful in my invention can be illustrated by the following:

Oxonol dyes:

(1) Bis[1 (p sulfophenyl) 3 methyl 2 pyrazolin-S-one] trimethineoxonol.

(2) Bis[1 (p sulfophenyl) 3 methyl 2 pyrazolin-S-one] pentamethineoxonol.

( 3) Bis 1,3-diethylbarbituric acid(5) lpentamethineoxonol.

(4) 1 methyl 1 [1 (p sulfophenyl) 3 methyl 2 pyrazolin 5 one] 3 [1 phenyl 3-methyl-2-pyrazolin-S-one] trimethineoxonol.

(5) [1,3 diethylbarbituric acid(5)][3 methyl 1-phenyl-2-pyrazolin-5 -one] trimethin eoxonol.

The S-phenylbenzothiazole dyes useful in practicing my invention can be represented by the following general formula:

4 k where R and R each represents an alkyl group, such as methyl, ethyl, fl-hydroxyethyl, etc. (e.g., an alkyl group containing from 1 to 2 carbon atoms), R represents a hydrogen atom, an alkyl group (e.g., methyl, ethyl, etc.), or an aryl group (e.g., phenyl, tolyl, etc., especially a mononuclear :aryl group of the benzene series containing from 6 to 7 carbon atoms), n represents a positive integer of from 1 to 2, X represents an acid radical, such as chloride, bromide, iodide, p-toluenesulfonate, benzene sulfonate, methylsulfate, ethylsulfate, perchlorate, etc., and Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus of the type customarily employed in thecyanine dye art, such as those of the ben zothiazole series, those of the benzoxazole series, those of the benzoselenazole series, those of the naphthothiazole series, those of the quinoline series, etc; Dyes of the type represented by Formula I above can advantageously be prepared according to methods already described in the prior art, such as in Brooker and Lincoln U.S. Patent 2,763,646, issued September 18, 1956.

The cyanine dyes containing a carboxyalkyl or a sulfo-T alkyl group useful in my invention can be represented by the following general formula:

II) Z R4 ,z,

d cH f= c-o11 :-oH)a-|=6 1 I R1 wherein R Z and it each have the values given above, R represents a carboxyalkyl or sulfoalkyl group (carboxymethyl, ,B-carboxyethyl, a-carboxyethyl, sulfomethyl, fl-sulfoethyl, etc.), R represents a hydrogen atom or an alkyl group (e.g., methyl, ethyl, etc.), d represents a positive-integer of from 1 to 2 and Z represents the nonmetallic atoms necessary to complete a heterocyclic nucleus of the type customarily employed in the cyanine dye art, for example, those nuclei listed above for Z. The dyes represented by Formula II above can advantageousl-y be prepared as described in Riester et al. U.S. Patent 2,213,995, issued September 10, 1940; Brooker and Smith U.S. Patent 2,231,659, issued February 11, 1941; Riester et al. U.S. Patent 2,238,231, issued April 15, 1941; and Sprague U.S. Patent 2,503,776, issued April 11, 1950.

The merocyanine dyes containing a carboxy or sulfo group useful in practicing my invention comprise the dyes represented by the following general formula:

(m) z Q\ R-1 i or1==orn, 1 o 1,-L ,=o-o=0 wherein R, n and Z each have the values given above, q represents a positive integer of from 1 to 3, L represents a methine group (i.e., a -CR'= group wherein R represents a hydrogen atom or an alkyl group, such as methyl, ethyl, etc.), and Q represents the non-metallic atoms necessary to complete a heterocyclic' nucleus of the type customarily employed in the merocyanine dye art, such as rhodanine, pyrazolinone, Z-thiohydantoin, 2-thio-2,4-' oxazolidinedione, etc. The dyes represented by Formula III above can be prepared according to the method shown in Brooker and White U.S. Patent 2,493,747, issued January 10, 1950, and Brooker and Keyes U.S. Patent 2,493,-

748, issued January 10, 1950.

The dyes represented by Formulas I, II and 111- above wherein Z and/or Z represent a heterocyclic nucleus containing a fused-on benzene ring can have simple substituents on this benzene ring, such as chlorine, bromine, methyl, ethyl, phenyl, methoxyl, ethoxyl, etc.

The oxonol dyes containing a pyrazolinone or barbituric acid nucleus can be prepared according to the methods shown in Gaspar U.S. Patent 2,274,782, issued March 3, 1942; Gaspar U.S. Patent 2,345,193, issued March 28, 1944; Keyes and Brooker U.S. Patent 2,611,696, issued September 23, 1952; and Van Dormael et al. U.S. Patent 2,621,125, issued December 9, 1952'. ,The effect obtained with the mixtures of light=absorbing .dyes and spectral sensitizing dyes according to my invem tioii varies depending uponthe quantity of light-absorbing dyes present, the ratio of sensitizing dye to lightabsorbing dye, the particular silver halide emulsion, etc.

The most useful combinations can be ascertained by simply preparing a series of test coatings varying the ratio of the sensitizing dye to absorbing dye in a particular emulsion. The quantity of a given dye will vary depending upon the purpose for which the emulsion is to be employed. In general, a sufficient quantity of absorbing dye should be employed so that the photographic silver halide emulsion has a contrast in its unsensitized region at least twice that for the sensitized region. Obv-iously, the exact amounts will vary depending upon the sensitizing dyes, light-absorbing dyes, etc., which are employed.

Especially useful results have been obtained when 4-[(1,3,3-trimethyl 2(3H) indolylidene)ethylidenel-3- methyl-l-phenyl-2,-pyrazolin-5-one is used as the sensitizing dye in combination with the light-absorbing oxonol dyes described above. Quite useful results have also been obtained when a thia-2'-cyanine dye containing at least one ,carboxyalkyl group is employed in combination with a light-absorbing dye of the oxonol dye series containing a 3-methyl-1-sulfophenyl 2 pyrazolin-S-one nucleus, although the results have not been as outstanding as in the case of the indolenine merocyanine dye mentioned above. It can be seen by reference to Fig. 4 of the accompanying drawings that this particular merocyanine dye has given quite outstanding results. The following examples will serve to illustrate more fully the manner of practicing my invention.

Example 1 A high contrast gelatinosilver-chlorobromide emulsion was sensitized with 3,3-dimethyl-5,5',9-triphenylthiacarbocyanine bromide (154 mg./mole AgX) giving the emulsion a sensitizing maximum at 630 III 1.. To portions of this emulsion were added varying amounts of the absorbing dye, bis[3-methyl-1-(p-sulfophenyl)-2-pyrazolin-S-onelpentamethine oxonol. The sensitivity of the emulsion to red light, transmitted by a Wratten No. 25 filter (i.e., a filter transmitting radiation only beyond about 585 me) was measured by exposure in an intensity scale sensitometer. The sensitivity to blue light, transmitted by a Wratten No. 47 filter (i.e., a filter transmitting only between about 370 and 515 m was meastired at the same time. Development was for 4 minutes in Kodak Developer D-19. The quantity of light- A absorbing dye used is given in the following table, together with the speed and gamma for the resulting coatings. The sensitivity or speed is expressed by the formula 100(1-log E) where E is the exposure in meter candle seconds of radiation from an incandescent light source of 3000 K. incident on the filter required to produce a density of 0.3 above fog.

Red Filter Blue Filter Coating Speed Gamma Speed Gamma Number Number (11)) Oo11trol) ..b. ;1 80 2.68 21 2.78 (b 14 g. a set ing ye per mole -79 2. 18 -26 2. 06 (c) 21 g. absorbing dye per mole. -109 1.07 37 1. 75

6 Example 2 A high contrast gelatino-silver-chlorobromide emulsion was sensitized by adding mg./mole AgX of 4[(l,3,3trimethy1 2(3H) indolylidene')ethylidenel-3- methyl-1-phenyl-2-pyrazolin-5-one from acetone solution. Then 7.0 g./mole of AgX of bisEB-methyl-l-(p-sulfophenyl)-2-pyrazolin-5-one]trimethine oxonol was added in neutralized aqueous solution, and the emulsion was coated in the usual manner at 250 square feet per mole of silver halide. The sensitivity of the coatings to green light was measured by exposure in an intensity scale sensitometer through a Wratten No. 12 filter (i.e., a filter transmitting only light beyond 495 m while the sensitivity to violet light was measured by exposure through a Wratten No. 35 filter (i.e., a filter transmitting light betweeen about 320-470 Hi and beyond 660 m Development was for four minutes in a developer (Kodak D-19) having the following composition:

Cold water to make one liter.

After fixing, washing and drying, the characteristic curves of the coatings were prepared as in Example 1..

The gamma of the film exposed through the No. 12 filter was 1.05, while that for the coating through the No. 35 filter was 2.25. These characteristic curves are shown in the drawings, which are discussed below.

Example 3 Results similar to those of Example 2 were obtained by replacing the sensitizing dye of that example with 150 g. of 3- 8-carboxyethyl-1-ethylthia-2-cyanine iodide.

While the above examples have been particularly con cerned with the use of silver chlorobromide emulsions because of their freedom from sensitivity in the bluegreen region, it is to be understood that my invention can also be employed with other photographic silver halide emulsions, such as gelatino-silver-chloride, -bromide, -chlorobrorniodide, -bromiodide, etc.

The ratio of the various silver halides in the elements of varying contrasts can also be varied depending upon the degree of contrast desired, speed desired, etc.

The emulsions can also be chemically sensitized by any of the accepted procedures. The emulsions can be digested with naturally active gelatin, or sulfur cornpounds can be added, such as those described in Shep pard U.S. Patents 1,574,944, issued March 2, 1926, and 1,623,499, issued April 5, 1927, and Sheppard and Brigham U.S. Patent 2,410,689, issued November 5, 1946.

The emulsions can also be treated with salts of the noble metals, such as ruthenium, rhodium, palladium, iridium and platinum, all of which belong to group VIII of the periodic table of elements and have an atomic weight greater than 100. Representative compounds are ammonium chloropalladate, potassium chloroplatinate and sodium chloropalladite, which are used for sensitizing in amounts below that which produces any substantial fog inhibition, as described in Smith and. Trivelli U.S. Patent 2,448,060, issued August 31, 1948, and as antifoggants in higher amounts, as described in Trivelli and Smith U.S. Patents 2,566,245, issued August 28, 1951 and pounds are potassium chloroaurite, potassium aurithio;

cyanate, potassium chloroaurate, auric trichloride and 2- aurosulfobenzothiazole methochloride.

The emulsions can also be chemically sensitized with reducing agents, such as stannous salts (Carroll US. Patent 2,487,850, issued November 15, 1949), polyamines, such as diethylene triamine (Lowe and Jones US. Patent 2,518,698, issued August 15, 1950), polyamines, such as spermine (Lowe and Allen US. Patent 2,521,925, issued September 12, 1950), or bis-(,B-aminoethyl) sulfide and its water-soluble salts (Lowe and Jones U.S. Patent 2,521,926, issued September 12, 1950).

The emulsions can also be stabilized with the mercury compounds of Allen, Byers and Murray U.S. Patent 2,728,663, issued December 27, 1955, Carroll and Murray US. Patent 2,728,664, issued December 27, 1955, and Leubner and Murray US. Patent 2,728,665, issued December 27, 1955.

The amounts of light-absorbing dyes used in the multicontrast emulsions of my invention can be varied, depending upon the degreeof contrast desired in the sensitized region. In general, I have found that from about 4 to 25 g./mo1e of silver halide of the light-absorbing dyes can be employed. The amounts of sensitizing dyes used can also be varied, depending upon the efiects desired. In general, from about to about 300 mg./mole of silver halide of the sensitizing dyes can be employed. The ratio of light-absorbing dye to sensitizing dye can likewise :be varied, although suflicient light-absorbing dye should be employed to give a contrast in the unsensitized region at least twice that for the sensitized region.

The accompanying drawings will serve to illustrate further the results obtained in my invention. Each figure in the drawings is a diagrammatic reproduction of the characteristic curves of the emulsions described in Examples 1 and 2 above. Figure 1 is a diagrammatic reproduction of the characteristic curves obtained from coating (a) of Example 1. Curve B of Fig. 1 represents the characteristic curve of the emulsion exposed with the Wratten No. 47 filter, i.e., to blue light. Curve A of Fig. 1 represents the characteristic curve of the emulsion exposed using the Wratten No. 25 filter, i.e., exposure to red light.

.In Fig. 2, curve C represents the characteristic curve of the emulsion of coating (b) of Example 1 exposed using the Wratten No. 47 filter, i.e., exposure to blue light, while curve D represents the characteristic curve of the same emulsion exposed using the Wratten No. 25 filter, i.e., exposure to red light.

In Fig. 3, curve F represents the characteristic curve of the emulsion of coating (0) of Example 1 exposed using a Wratten No. 25 filter, i.e., exposure to red light, while curve B represents the characteristic curve of the emulsion of coating (c) of Example 1 exposed using a Wratten No. 47 filter, i.e., exposure to blue light.

It can be readily seen by comparison of the characteristiccurves of Figs. 1, 2 and 3 that the curves give a more accurate evaluation of the characteristics of the multicontrast emulsions than the gamma figures set forth in Example 1.

In Fig. 4, curve G represents the characteristic curve of the emulsion of Example 2 exposed using a Wratten No. 35 filter, i.e., exposure to violet light, while curve H represents the characteristic curve of the same emulsion exposed using a Wratten No. 12 filter, i.e., exposure to greenlight. The long scale of the curve obtained by exposure to green light is quite apparent, and it can be seen that the sensitivities through the two filters are quite similar, so that it is easy to adjust exposures to give any'required gamma between these two limits. In addition, in this type of film using a single emulsion, the relative contrasts are almost independent of processing conditions.

It can be seen from the characteristic curves shown in'the drawings that my invention can be used when the emulsion has been sensitized either for the green or red regions of the spectrum. Since most emulsions have an; inherent sensitivity lying in the blue region of the spee trum, it is obvious that the sensitizing dye employed;

should generally have its maximum sensitization beyond the blue region of the spectrum. The combination illus trated in Example 2 above has been found particularly. outstanding in that an exceptionally wide range of exposures and varying contrasts is provided.

As shown in the above examples, the oxonol dyes can be added to the emulsions in the form of their neutral aqueous solutions. Thus, the acidic dyes are at least partially neutralized. Neutralization can be effected by the usual alkaline or basic agents, such as sodium hy-v droxide, potassium hydroxide, sodium carbonate, potassium carbonate, triethylamine, pyridine, etc. It is to be understood that the term oxonol dye as used in the foregoing specification and claims includes either the acid or base form of the dye. Also, the term su1fo" as used in the foregoing specification is intended to include not only the --SO H group but the salt forms of this group.

While the term a barbituric acid nucleus is generally understood in the sensitizing dye art to include 2- thiobarbituric acid, it is not so defined in the present invention since dyes derived from 2-thiobarbituric acid show an undesirable desensitizing action. The foregoing description and claims should be interpreted accordingly.

As indicated above, the alkyl group represented by R, can be a substituted alkyl group, such as p-hydroxyethyl, carboxymethyl, fl-carboxymethyl, sulfomethyl, /3-sulfoethyl, etc. With respect to the dyes represented by Formula II above, those dyes wherein R is a sul-foalkyl or carboxyalkyl group have been found to provide quite useful results. 4-[(l,3,3-trimethyl-2(3H)-indolylidene)- ethylidene] 3 methyl-l-phenyl-Z-pyrazolin-S-one has. been found to be among the most useful of all sensitizing dyes employed in my invention.

What I claim as my invention and desire secured by Letters Patent of the United States is:

l. A photographic silver chlorobromide emulsion sensitized with from about 5 to 300 ing/mole, based on th amount of silver chlorobromide, of a 3,3-dialkyl-5,5',9- triphenylthiacarbocyanine salt wherein the alkyl groups. contain from 1 to 2 carbon atoms, said sensitized silver. chlorobromide emulsion containing from 4 to 25 g./ mole, based on the amount of silver chlorobromide, of a his [3 methyl 1 (sulfophenyl) 2 pyrazolin 5 one] pentamethine oxonol dye, said oxonol dye having its maximum absorption in substantially the same region of; the spectrum as said sensitizing dye, the amounts of said sensitizing dye and said light-absorbing dye being such that said emulsion has a contrast for the unsensitized region at least twice that for the sensitized region.

2. A photographic silver chlorobromide emulsion sensitized with from about 5 to 300 mg./ mole, based on the amount of silver chlorobromide, of 3,3'-dimethyl5,5',9- triphenylthi-acarbocyanine bromide, said sensitized 'emul sion containing from about 4 to 25 g./mole, based on the amount of silver chlorobromide, of bisI3-methyl-1- (p-sulfophenyl)-2-pyrazolin5-one]pentamethiue oxonol .as a light-absorbing dye, the amounts of said sensitizing dye and said oxonol dye being such that said emulsion has a contrast for the unsensitized region of the spectrum at least twice that for the sensitized region.

3. A photographic silver chlorobromide emulsion sensitized with from about 5 to 300 mg./mole, based on the amount of silver chlorobromide, of 3-;8-carboxyethyl-1'- ethylthia-2'-cyanine iodide, said sensitized emulsion containing from about 4 to 25 g./ mole, based on the amount of silver chlorobromide of bis[3-rnethyl-l-(p-sulfophenyl)-2-pyrazo1in-5-one]trimethine oxonol as a light-absorbing dye, the amounts of said sensitizing dye and said light-absorbing oxonol dye being such that said emulsion has a contrast for the unsensitized region of the spectrum at least twice that for the sensitized region.

and (2) an acid cyanine dye selected from those represented by the following general formula:

is-nl wherein R and R each represents a member selected from the group consisting of methyl, ethyl, and fi-hydroxyethyl, R represents a member selected from the group consisting of a hydrogen atom, an alkyl groupcontaining from 1 to 2 carbon atoms and a mononuclear aryl group of the benzene series containing from 6 to 7 carbon atoms, R represents a member selected from the group consisting of a carboxyalkyl group containing from 2 to 3 carbon atoms and a sulfoalkyl group containing from 1 to 2 carbon atoms, R represents a member selected from the group consisting of a hydrogen atom and an alkyl group containing from 1 to 2 carbon atoms, X represents an acid radical, d and n each represents a positive integer of from 1 to 2, and Z and Z each represents the non metallic atoms necessary to complete a heterocyclic nucleus selected from the group consisting of those of the benzothiazole series, those of the benzox-azole series, those of the benzoselenazole series, those of the naphthothiazole series and those of the quinoline series, said sensitized photographic silver halide emulsion containing from about 4 to 25 g./mole, based on the amount of silver halide, of a light-absorbing oxonol dye selected from the class consisting of a trimethine oxonol dye and a pentamethine oxonol dye, said oxonol dye having a 3-methyl-1-(sulfophenyD-S-pyrazolinone nucleus attached to one end of the methine chain through the 4-position of said 3-methyll-(sulfophenyl)-5-pyrazolinone nucleus, and attached to the other end of said methine chain a second nucleus selected from the class consisting of a 5-pyrazolinone nucleus and a 2,4,6-triketohexahydropyrimidine nucleus, said light-absorbing oxonol dye having its maximum absorption in substantially the same region of the spectrum as said sensitizing dye, the amounts of said sensitizing dye and said light-absorbing dye being such that said emulsion has a contrast for the unsensitized region of the spectrum at least twice that for the sensitized region, said sensitizing dye having its maximum absorption beyond about 480 m 5. A photographic silver halide emulsion as defined in claim 4 wherein the silver halide is silver chlorobromide.

6. A photographic silver chlorobromide emulsion sensitized with from about 5 to 300 mg./mole, based on the amount of silver chlorobromide, of a spectral sensitizing dye selected from those represented by the following general formula:

wherein R and R each represents a member selected from the group consisting of methyl, ethyl, and B-hydroxyethyl, R represents a member selected from the group consisting of a hydrogen atom, an alkyl group containing from 1 to 2 carbon atoms and a mononuclear aryl group of the benzene series containing from 6 to 7 carl0 bonatoms, Xi represents an acid radical, n represents a positive integer of from 1 to 2, and Z represents the nonmetallic atoms necessary to complete a heterocyclic nucleus selected from the group consisting of those of the benzothiazole series, thos of the benzoxazole series, those of the benzoselenazole series, those of the naphthothiazole series and those of the quinoline series, said sensitized photographic emulsion containing from about 4 to 25 g. mole, based on the amount of silver chlorobromide, of a light-absorbing oxonol dye selected from the class consisting of a trimethine oxonol dye and a pentamethine oxonol dye, said oxonol dye having a 3-methyl-1-(sulfophenyl)-5-pyrazolinone nucleus attached to one end of the methine chain through the 4-position of said 3-methyll-(sulfophenyl)-5-pyrazolinone nucleus, and attached to the other end of said methine chain a second nucleus selected from the class consisting of a 5-pyrazolinone nucleus and a 2,4,6-triketohexahydropyrimidine nucleus,

said light-absorbing oxonol dye having its maximum absorption in substantially the same region of the spectrum as said sensitizing dye, the amounts of said sensitizing dye and said light-absorbing dye being such that said emulsion has a contrast for the unsensitized region of the spectrum at least twice that for the sensitized region, said sensitizing dye having its maximum absorption beyond about 480 m 7. A photographic silver chlorobromide emulsion sensitized with from about 5 to 300 mg./rnole, based on the amount of silver chlorobromide, of a sensitizing dye selected from those represented by the following general formula:

, ,Z R4 lea- 16(l =orroH),, 1 o-o11(=bo11)=6 N-R, wherein R represents a member selected from the group consisting of methyl, ethyl, and [i-hydroxyethyl, R represents a member selected from the group consisting of a carboxyalkyl group containing from 2 to 3 carbon atoms and a sulfoalkyl group containing from 1 to 2 carbon atoms, R represents a member selected from the group consisting of a hydrogen atom and an alkyl group containing from 1 to 2 carbon atoms, d and n each represents a positive integer of from 1 to 2, and Z and Z each represents the non-metallic atoms necessary to complete a heterocyclic nucleus selected from the group consisting of those of the benzothiazole series, those of the benzoxazole series, those of the benzoselenazole series, those of the naphthothiazole series and those of the quinoline series, said sensitized photographic emulsion containing from about 4 to 25 g./ mole, based on the amount of silver chlorobromide, of a light-absorbing oxonol dye selected from the class consisting of a trimethine oxonol dye and a pentamethine oxonol dye, said oxonol dye having a 3-methyl-1-(sulfophenyl)-5-pyrazolinone nucleus attached to one ends of the methine chain through the 4-position of said B-methyl-l-(sulfophenyl)-5-pyrazolinone nucleus, and attached to the other end of said methine chain a second nucleus selected from the class consisting of a S-pyrazolinone nucleus and a 2,4,6-tniketohexahydropyrimidine nucleus, said light-absorbing oxonol dye having its maximum absorption in substantially the same region of the spectrum as said sensitizing dye, the amounts of said sensitizing dye and said light-absorbing dye being such that said emulsion has a contrast for the unsensitized region of the spectrum at least twice that for the sensitized region, said sensitizing dye having its maximum absorption beyond about 480 mg.

8. A photographic silver chlorobromide emulsion sensitized with from about 5 to 300 mg./rnole, based on the amount of silver chlorobromide, of a 3-fi-carboxyethyll'-al'kylthia-2-cyanine salt wherein the alkyl group contains from 1 to 2 carbon atoms, said sensitized emulsion containing from about 4 to 25 g./mole, based on the amount of silver chlorobromide, of a light-absorbing oxonol dye selected from the class consisting of a trimethine oxonol dye and a pentamethine oxonol dye, said oxonol dye having a S-methyl-l-(sulfophenyl)-5-pyrazolinone nucleus attached to one end of the methine chain through the 4-position of said 3-methyl-1-(sulfophenyl)-5-pyrazolinone nucleus, and attached to the other end of said rnethine chain a second nucleus selected from the class consisting of a S-pyrazolinone nucleus and a 2,4,6-triketohexahydropyrimidine nucleus, said lightaabsorbing oxonol dye having it maximum absorption in substantially the same region of the spectrum as said sensitizing dye, said sensitizing dye having its maximum absorption beyond about 480 my, the amounts of said sensitizing dye and said light-absorbing oxonol dye being such that said emulsion has a contrast for said unsensitized region of the spectrum at least twice that forthe sensitized region.

" 7 References (Iited in the file of this patent UNITED STATES PATENTS 2,213,995 Riester et a1 Sept. 10, 1940 2,533,472 Keys et al. Dec. 12, 1950 2,588,615 Capstafi Mar. 11, 1952 OTHER REFERENCES 

4. A PHOTOGRAPHIC SILVER HALIDE EMULSION SENSITIZED WITH FROM ABOUT 5 TO 300 MG./MOLE, BASED ON THE AMOUNT OF SILVER HALIDE, OF A SPECTRAL SENSITIZING DYE SELECTED FROM THE GROUP CONSISTING OF (1) A NEUTRAL CYANINE DYE SELECTED FROM THOSE REPRESENTED BY THE FOLLOWING GENERAL FORMULA: 